Developing B cells undergo regulated cell division and apoptosis in response to their success in assembling the genes encoding their antigen receptors. In addition, the specificity of these receptors is monitored and developing cells with the potential for self-specificity are signaled to either edit their receptors or undergo apoptosis. This research proposal focuses on a protein tyrosine kinase, c-Abl, which our preliminary data and the experiments of others lead us to believe may be involved in these key developmental processes, c-Abl is the cellular homologue of v-Abl, the transforming gene of the Abelson Murine Leukemia Virus (A-MuLV) which causes acute B cell leukemia in mice. In humans, c-Abl is involved in a disease-associated chromosomal translocation which generates the BCR-Abl fusion protein in several forms of leukemia. We propose to test hypotheses regarding the biological functions of the Abl kinase in developing B cells and its role in transformation through pursuit of two specific aims. First, we will perform experiments aimed at understanding how v-Abl disrupts signaling pathways, blocks differentiation, and prevents the apoptosis of leukemic murine pro-B cell lines. These experiments will use a newly available specific inhibitor of the Abl tyrosine kinase, STI-571 (Gleevec), DNA microarrays, and a recently-developed retroviral cDNA cloning strategy called CPR. Second, we will test hypotheses regarding the role of c-Abl in the regulation of cell proliferation, viability, gene expression, pre-BCR signaling, allelic exclusion, receptor editing and clonal deletion during normal murine B cell development. We will attempt to identify the critical targets of the Abl kinase involved in these processes. These experiments will take advantage of primary cell culture systems and STI-571, as well as available null mutations in ARG (Abl-related gene) and c-Abl. These studies are significant because of the involvement of c-Abl in the etiology of chronic myelogenous leukemia and acute lymphocytic leukemia in humans and the growing use of the Abl inhibitor STI-571 in the clinical treatment of various malignancies.